The present invention relates to a device for determining a strength profile of a human limb. The device according to the invention enables the determination of a strength profile, for e.g. an arm or a leg of a human subject. The strength profile can be presented as a table or diagram illustrating the forces and torques the human limb in question can exercise in different directions in a suitable coordinate system. The device according to the invention is a useful tool in ergonomic, orthopaedic and research work.
It is previously known with a number of different devices which can determine the strength profile of a human limb.
Accordingly, in an study published in Journal of Neurophysiology, Vol. 62, NO. 6, December 1989, Buchanan et al. disclose force measurements using a 3 degrees-of-freedom load cell for measuring the force at the wrist of a human subject. The disclosed device consisted of six pairs of strain gauges which decomposed forces into flexion-extension, up-down (or varus-valgus), and supination-pronation components. The disclosed device enabled different muscles to be examined in eight torque directions. During the experiments, the subject was seated with his arm in the load apparatus, watching a target on a monitor. As each target appeared on the monitor, the subject was to manipulate a cursor, by means of exercising a force on the load apparatus with his/her arm,to be within target boundaries on the screen and to maintain the cursor in this position for 2,5 seconds.
Furthermore, in a Thesis in partial fulfilment of the degree of Licentiate of Engineering, Paper II, Chalmers University of Technology, Gothenburg 1996, Makhsous et. al. disclose the determination of strength profiles using a force device which consists of two short tubes of stainless steel connected to each other by four smaller tubes of spring steel with longitudinal slits. These small tubes are resilient enough to allow the measurement of the deformation caused by translating the inner tube relative to the outer tube in radial direction. In order to measure the deformation in the small tubes, two strain gauges are bonded to the inner and outer surfaces of each tube, so that both compression and elongation on both sides of the tube walls can be detected.
However, the previously known devices for determining a strength profile of a human limb do not provide the possibility to determine forces and torques in all three dimensions in a three-dimensional coordinate system.
Furthermore, some of the previously known devices have a complicated design and function, and can accidentally be broken or disturbed by a human subject.
Accordingly, the first object of the present invention is to provide a simple, inexpensive, reliable and robust device for determining a strength profile of a human limb, which device is able to determine forces in any direction, and preferably also torques around axes extending in any direction, in a three-dimensional coordinate system.
In accordance with claim 1, this first object is achieved by means of a device comprising a first tubular member and a supporting means intended to be suspended in a fixed position in relation to a coordinate system. The first tubular member is arranged for holding the human limb and for being in contact with the supporting means via at least one force sensor means arranged for detecting forces exercised by the human limb on the first tubular member in directions in the coordinate system when determining the strength profile. Thereby, the coordinate system in three-dimensional and has x-, y and z-axes and the force sensor means is/are arranged for detecting forces along each of the x-, y- and z-axes.
Further objects of the present invention will become evident from the following description, and the features enabling these further objects to be achieved are listed in the dependent claims.